The present invention relates to an outboard motor, and in particular, to an improvement to a blade casing.
For a conventional outboard motor, which has a propeller extending downward from a bottom of a ship so as to be under water, there is a possibility that the propeller is damaged by being caught in seaweed or cord-like objects such as a net or by being brought into contact with sands or rock, resulting in reduced thrust. The accidental contact of a human with the propeller results in injury or death.
Japanese Patent Application Laid-Open No. 12(2000)-168687 discloses a housing provided to the periphery of a propeller so as to prevent a propeller extending into water from being caught in seaweed and the like. However, since an opening of the housing is oriented to the forward running direction of a ship, debris and cord-like objects are likely to enter the housing. Therefore, there is the possibility that the propeller and a propeller shaft incur damage.
A water jet propulsion outboard motor disclosed in Japanese Patent Application Laid-Open No. 7(1995)-89489 reverses a water jet causing a large energy loss upon the reverse running of a ship. With lowered thrust during reverse running, the maneuverability of the ship when getting close to the shore is inferior to that of a conventional propeller outboard motor. Furthermore, a reverser employed to reverse the water jet makes the outboard motor elongated in a longitudinal direction of the ship.
In view of the conventional problems as described above, the present invention has an object of providing a small and light-weight safety outboard motor with enhanced thrust efficiency.
In order to achieve the above object, an outboard motor according to a first aspect of the present invention comprises: a driving motor; a switching device for switching rotation of a drive shaft of the driving motor between normal and reverse directions; the impeller rotated with a driven shaft connected to the switching device; and a blade casing including a first duct member having a first opening through which water is sucked from outside when the impeller is rotated in the normal direction and a second duct member for enclosing the impeller, connected with the first duct member, the second duct member having a second opening though which water is sucked from the outside when the impeller is rotated in the reverse direction.
According to the first aspect, the direction of rotation of the impeller can be changed by the switching device. When the impeller is rotated in the normal direction, water is sucked through the first opening from the outside and is discharged through the second opening. When the impeller is rotated in the reverse direction, water is sucked through the second opening from the outside and is discharged through the first opening.
Therefore, in the case where the first opening is provided so as to be oriented in a forward direction of a ship whereas the second opening is provided so as to be oriented in a backward direction of the ship, the reverse rotation of the impeller causes the water to be jetted out through the first opening toward the forward direction of the ship, so that the ship can run in the backward direction.
An outboard motor according to a second aspect of the present invention is the outboard motor according to the first aspect, wherein the second opening is adjacent to the impeller.
According to the second aspect, since the second opening is adjacent to the impeller, the blade casing extending in a backward direction of the ship can be shorter, reducing the weight of the outboard motor. Moreover, water flow resistance within the blade casing is reduced.
An outboard motor according to a third aspect of the present invention is the outboard motor of the first aspect, wherein the blade casing includes a bearing rotatably supporting the driven shaft.
An outboard motor according to a fourth aspect of the present invention is the outboard motor of the third aspect, wherein the bearing is provided on the first duct member.
According to the above aspects, since the switching device is fixed to the bearing provided on the first duct member, length of the driven shaft is reduced and the outboard motor becomes compact as well as light-weight.
An outboard motor according to a fifth aspect of the present invention is the outboard motor of the third aspect, wherein the bearing is fixed to a support extending inward from an inner surface of the blade casing.
An outboard motor according to a sixth aspect of the present invention is the outboard motor of the fifth aspect, wherein the bearing rotatably supports an end of the driven shaft.
According to the above aspects, since both ends of the driven shaft are rotatably supported, vibration due to rotation is reduced. Moreover, straightening effects for a water jet can be obtained by the support.
An outboard motor according to a seventh aspect of the present invention is the outboard motor of the fifth aspect, wherein the support is a guide blade.
According to the seventh aspect, since a plurality of guide blades are provided behind the impeller, a swirl flow which is pressurized with the impeller is straightened into a linear flow to be jetted out through the second opening, contributing to increased thrust.
An outboard motor according to an eighth aspect of the present invention is the outboard motor of the third aspect, wherein the switching device is fixed to the bearing.
An outboard motor according to a ninth aspect of the present invention is the outboard motor of the eighth aspect, wherein the drive shaft penetrates through the blade casing.
According to the above aspects, since the switching device is arranged within the blade casing, the driven shaft is shortened, reducing vibration. Moreover, the outboard motor is reduced in size as well as weight.
An outboard motor according to a tenth aspect of the present invention is the outboard motor of the first aspect, wherein the impeller includes a cylindrical hub and axial flow blades; and an inner surface of the second duct member adjacent to the radially outer edges of the axial flow blades, is cylindrical.
According to the tenth aspect, since the amount of discharged water upon normal rotation of the axial flow blades is approximately equal to that upon reverse rotation, the thrust obtained when the ship runs in a reverse direction can be equivalent to that obtained when the ship runs in a forward direction. By switching the rotation of the axial flow blades between normal and reverse directions, a running direction of the ship can be changed to a forward/backward direction within a short period of time.
An outboard motor according to an eleventh aspect of the present invention is the outboard motor of the first aspect, wherein the impeller comprises a conical hub and diagonal flow blades; and an inner surface of the second duct member adjacent to the radially outer edges of the diagonal flow blades, is conical.
According to the eleventh aspect, since the front suction portions of the radially outer edges of the diagonal flow blades for guiding an entering water flow are wide open, suction efficiency is improved to increase thrust during running in a forward direction. Moreover, balance efficiency is enhanced with a plurality of the diagonal flow blades.
An outboard motor according to a twelfth aspect of the present invention is the outboard motor of the first aspect, wherein the impeller comprises a conical hub and axial flow blades; and an inner surface of the second duct member adjacent to radially outer edges of the axial flow blades, is cylindrical.
According to the twelfth aspect, since the hub has a conical shape, the suction performance with the axial flow blades can be close to that obtained with the diagonal flow blades.
An outboard motor according to a thirteenth aspect of the present invention is the outboard motor of the first aspect, wherein the blade casing is detachably divided.
An outboard motor according to a fourteenth aspect of the present invention is the outboard motor of the thirteenth aspect, wherein the blade casing is divided into one on a first opening side and the other on a second opening side.
An outboard motor according to a fifteenth aspect of the present invention is the outboard motor of the thirteenth aspect, wherein the blade casing is divided by a plane including the drive shaft and the driven shaft.
According to the above aspects, the attachment, removal, inspection and repair of the outboard motor are facilitated.
An outboard motor according to a sixteenth aspect of the present invention is the outboard motor of the thirteenth aspect, wherein the impeller is a propeller.
An outboard motor according to a seventeenth aspect of the present invention is the outboard motor of the sixteenth aspect, wherein the outboard motor further comprises: a housing for mounting the driving motor; and an attachment member for fixing the blade casing to the housing, detachably attached to the housing.
According to the above aspects, even in an existing outboard motor with the propeller extending downward from a bottom of the ship, the propeller is protected during running on shallows such as in the vicinity of the shoreline or on a river because the blade casing encloses the propeller and the lower casing. Moreover, accidental contact with the propeller resulting in injury or death is prevented.
With a suction port of the blade casing oriented in a downward direction, the amount of debris and cord-like objects entering the suction port can be reduced. Therefore, the propeller is not easily caught in debris and cord-like objects.
Furthermore, since the blade casing is divided into two parts, i.e., right and left parts, and detachably attached via the attachment member, the blade casing can be readily employed on an existing outboard motor and propeller, and facilitates the inspection and repair of the propeller.